Microelectronic devices typically comprise of an integrated circuit diode die encompassed in a package having a plurality of external leads permitting electrical attachment to a printed circuit board. These microelectronic devices are available as commercial devices, and some are available as high reliability devices such as used in military applications, including those integrated in space environments, such as satellites, space vehicles and solar panels. In space environments, microelectronic devices need to withstand extreme thermal cycling, such as from −197 C. to +150 C.
All materials have a coefficient of thermal expansion, which is a thermal index indicating the relative degree a material expands or contracts as a function of temperature. Materials contract as they are cooled, and expand as they are warmed. Therefore, microelectronic devices employ materials with similar coefficients of thermal expansion that they can withstand extreme thermal cycling. Portions of the device having similar coefficients of thermal expansion are secured to one another using adhesive, paste, solder and so forth to avoid separation during thermal cycling.
In space applications, one typical integrated circuit includes a solar cell diode which may be joined to a solar cell panel. These solar cell diodes are subject to some of the most severe thermal cycling environments given their exposure to the sun and subsequent shading therefrom numerous times over their life cycle. Conventionally, these solar cells devices are comprised of glass and are soldered or welded to the solar panel, and interconnected to other circuits using rigid materials, such as rigid axial leads. These rigid leads can tolerate the extreme thermal cycling for a period of time, but have a limited life cycle. These axial leaded devices were designed for solder attachment to the solar panel. The solder joint in this design has limited thermal cycling capability due to thermal expansion mismatch, solder re-crystallization, and solder creep. Cracking it the solder joint is then followed by an electrical disconnect with the circuit.
More recently, solar panel manufacturers have switched to attaching the axial leaded devices using a welded connection. The axial leads do not lend themselves to welding easily. Solar panel manufactures struggle with the weld attachment. Welding flat leads to round axial leads causes reliability and weld consistency problems. An easier more reliable method is desired.
Integrated circuits generate heat during operation due to conduction losses. This heat must be dissipated from the device for proper functioning. Axial leaded glass diodes in particular are very difficult to heat sink to the panel and remove the heat efficiently. Solar panel manufactures have been struggling with thermal problems associated with the axial leaded glass diodes. A device that can be more efficiently heat sunk is desired.
There is desired an improved microelectronic device adapted to withstand extreme thermal cycling, such as that encountered in a space environment.